import java.util.Scanner;

/**
 * Created with IDEA
 * author:ju bai
 * Date:2021/4/17
 * Time:11:15
 **/
public class Main1 {
    /**
     * 每日一题-不为二
     * 规律如下：
     * ⚪⚪××⚪⚪
     * ⚪⚪××⚪⚪
     * ××⚪⚪××
     * ××⚪⚪××
     * ⚪处为放蛋糕的位置
     *
     * @param args
     */
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        while (scanner.hasNext()) {
            int h = scanner.nextInt();
            int w = scanner.nextInt();
            int[][] arr = new int[h][w];
            for (int i = 0; i < h; i++) {
                //当行列都满足类似0，1，4，5//中间隔两个（2，3）
                if (i % 4 == 0 || i % 4 == 1) {//0，1//4，5
                    for (int j = 0; j < w; j++) {
                        if (j % 4 == 0 || j % 4 == 1) {
                            arr[i][j] = 1;
                        }
                    }
                } else {
                    for (int j = 0; j < w; j++) {
                        //当行不满足时，把列为（2，3）的标记
                        if (j % 4 == 2 || j % 4 == 3) {
                            arr[i][j] = 1;
                        }
                    }
                }
            }
            //统计满足条件的个数
            int count = 0;
            for (int i = 0; i < h; i++) {
                for (int j = 0; j < w; j++) {
                    if (arr[i][j] == 1) {
                        count++;
                    }
                }
            }
            System.out.println(count);
        }
    }
}
